C型换热器管外流体两相自然循环数值模拟

建立了简化的C型换热器管外流体CFD分析模型,模拟了反应堆安全壳内置换料水箱（IRWST）中典型气液两相自然循环特性。首先用公开发表文献中的试验数据对计算方法进行校验,计算中采用的湍流模型、壁面沸腾模型等能较好地捕捉主流流体升温特性、两相自然循环特性。结果表明：C型换热器增加了管外流体流场分布的不均匀性,提高了冷、热流体间的搅混强度,有助于降低管外流体温度差,增加大容积水池内的自然循环能力;但由于壁面对气泡的阻滞作用,换热器弯管及水平管局部区域空泡份额最大,发生了气泡聚集。计算结果可为非能动余热排出换热器的设计提供支持。     

压水堆余热排出换热器性能研究

以压水堆余热排出系统为对象,建立管壳式换热器的数学模型。与换热器设计软件HTRI的计算结果进行对比,结果表明该模型可以准确预测管壳式换热器的管壳侧出口温度。总传热系数敏感性计算表明,该参数随管壳侧流量变化而变化,在换热器性能预测时不能当作常数处理,应与工况进行耦合计算。当管壳侧体积流量小于1000 m3/h时,总传热系数对流量较为敏感;当体积流量大于1000 m3/h时,流量的影响则相对较弱。该模型为预测换热器其他工况的换热性能提供基础,为换热设备调试提供指导,为核电厂设计验证及高效安全运行提供可靠依据。     

竖直和水平圆管换热器在内热源液池内的两相换热特性

针对溶液堆整体模拟试验模型的结构尺寸和运行工况,建立了内热源液池内自然对流和鼓泡驱动同时作用下竖直和水平圆管换热器的两相流动和换热模型,进行了相应的数值模拟计算.数值计算得到不同加热强度和鼓泡流量下的对流换热性能,与相应试验结果进行了比较分析.利用相似理论和量纲分析,推导了内热源液池内两相流动换热的无因次准则关系式,根据数值计算结果总结出换热Nu数的经验关系式.最后,分析比较了竖直和水平圆管换热器的两相对流换热特性,为溶液堆内换热器设计和布置提供理论参考.     

氦气轮机发电系统动态仿真模型

采用一维流动与传热模型对氦气轮机发电系统的涡轮机、压气机、换热器、阀门、管道以及轴转速模型进行模拟,采用MATLAB编制了氦气轮机闭式循环系统的动态计算程序.采用该程序计算分析了复气轮机系统电网负荷丧失事故工况以及主换热器换热量减少瞬态工况下氦气轮机发电系统氦气流量、温度、轴转速、功率以及压气机喘振裕度等参数的变化.结...     

非能动余热排出换热器换热能力数值分析

基于多孔介质模型,对AP1000非能动余热排出换热器(PRHR-HX)运行初始阶段进行了数值模拟。一回路的入口温度及流量采用RELAP5的计算结果,并以此作为CFD计算的边界条件。采用多孔介质模型处理C型管束区,添加管束区分布阻力。通过商业CFD软件FLUENT计算得到安全壳内置换料水箱(IRWST)侧冷却剂的三维温度及速度分布,通过用户自定义函数UDF完成一回路侧与IRWST侧的耦合换热计算,获得一回路温度分布及换热量。计算结果表明,随着IRWST内冷却剂温度升高,换热器热负荷降低,并出现明显的热分层现象,同时证明采用多孔介质模型与耦合换热计算是分析PRHR/IRWST系统瞬态热工水力特性的有效方法。     

微小通道内流动及气溶胶沉积特性实验研究

事故后气溶胶通过安全壳微小通道穿透会发生滞留现象，在不同载气流动状态下，主导沉积机制不同，会影响气溶胶的穿透率，因此需要研究微小通道内气溶胶的载气流动特性及气溶胶沉积特性。本文建立了微小通道气溶胶穿透与滞留实验装置，开展了雷诺数为40～3 600的载气流动与气溶胶沉积实验研究。在雷诺数约为700时，微小通道内会发生层流转捩。层流流动下，在大突缩比的矩形微通道中，随着雷诺数的增大，入口碰撞效应减弱，穿透率增大；小突缩比薄壁毛细管微通道入口效应弱，随着雷诺数的增大，气溶胶几乎完全穿透。在雷诺数为800～3 600的湍流流动下，气溶胶沉积主要处于涡流扩散-碰撞区及惯性主导区，受到湍流涡的影响气溶胶穿透率随雷诺数的增大而减小。     

钒球14 MeV中子的泄漏能谱测量

建立了厚度为 1 0 5cm的金属钒球基准实验装置。钒的纯度为 99 9%。用NE 2 1 3谱仪测量了d T中子的 0 75～ 1 5MeV泄漏中子能谱 ,能量大于 0 75MeV的中子的穿透率为 0 84± 0 0 3 ,中子能谱实验误差为 5 %～ 7%。用MCNP/ 4AMonte Carlo程序和FENDL 2库核数据进行了模拟计算 ,并与实验结果进行了比较     

千瓦级2 K超流氦板翅式换热器初步设计优化

本文采用分布参数法对1 000 W@2 K低温系统配套的50 g/s流量2 K换热器进行了设计计算。利用加权系数法提出了换热器综合优化指标,随后采用遗传算法进行优化,并根据工程需要从多个侧重点对换热器进行优化,获得了一系列优化方案,从中选择了侧重换热效率的方案作为初步设计结果。在该结果的基础上,进一步采用了CFD数值仿真校核,验证了初步设计结果的准确性。优化后换热器的换热效率为844%,压降为22216 Pa,体积为0022 1 m3。     

求解深穿透问题的能量偏倚减方差方法

采用堆用蒙特卡罗程序（RMC）进行反应堆屏蔽计算时，面临着深穿透的技术难题。通过分析中子在屏蔽层中的输运过程，证明了各能群的中子都满足穿透率守恒。在RMC中开发了基于穿透率守恒的自适应局部减方差方法，该方法可以快速计算出指数重要性函数和等梯度重要性函数，对中子的空间位置和能量值同时进行偏倚，高效地求解出深穿透区域的能谱分布。用工程常用的混凝土和水屏蔽层进行测试，计算结果证明:该方法可以高效地求解深穿透问题，提高RMC的计算效率。      

超临界二氧化碳在印刷电路板式换热器内的流动换热特性研究

印刷电路板式换热器（PCHE）是一种微通道换热器，具有换热效率高、耐高温、耐高压等优势，可广泛应用于海洋工程、核能、光热发电等领域。本文采用数值模拟的方法，计算了跨拟临界点超临界二氧化碳（SCO₂）在印刷电路板式换热器内的流动换热特性。结果表明：SCO₂流体温度达到拟临界温度时，流通截面内流体温度分布最均匀，因为此时流体的有效导热系数最大；SCO₂侧对流换热热阻在总热阻中占比最大，其次为导热热阻，水侧对流换热热阻最小；采用等效厚度法计算得到的导热热阻偏大；雷诺数越大，在拟临界温度附近换热强化的程度越大。     

多孔介质方法在池式快堆系统分析软件SAC-CFR三维钠池计算模型中的应用

为准确分析池式快堆热钠池内的热工水力学特性,在已开发出的用于池式快堆系统分析的钠池三维计算模型的基础上,应用多孔介质方法建立钠池内中间热交换器、主泵、事故热交换器及屏蔽柱模型,完成了含有多孔介质模型和复杂几何边界的钠池三维计算模型开发。将该模型嵌入池式快堆系统分析软件SAC-CFR后,分析了中国实验快堆在稳态运行和紧急停堆工况下钠池内的流场分布,初步证明了所采用的多孔介质模型的合理性,为下一步非能动余热排出系统模型的开发做准备。     

自然循环换热器壳侧传热及流动的数值模拟

为分析换热器的求解模型和内部结构的不同对传热和流动特性的影响,用等效自然循环换热器的模型进行多种变换。用Fluent软件对等效模型进行非稳态数值模拟,研究其传热和流动特性。通过比较分析不同模型的温度场和流场的变化,对该换热器的传热过程和自然对流情况有较深刻的认识。结果表明：自然循环换热器的传热管内外温差较大,且流动较复杂,选用湍流模型计算更为合理;传热管位置的不对称性,引起左右两侧传热和流动的不对称性,使得流体相互影响,增强了自然对流作用;传热管的形状由直管变为C型弯管,结构的复杂性在一定程度上增强了流体温度分布和流动的不规则性,使得湍流强度增加,致使换热效果得到改善。     

基于遗传算法的闭式非能动安全壳热量导出系统排热能力优化

以闭式非能动安全壳热量导出系统（PCCS）概念方案为研究对象，基于一维两相均相流模型建立了评价该系统排热能力的物理模型，并开发了相应的计算程序；开发了基于遗传算法的优化设计程序；利用所开发的优化设计程序，对闭式PCCS概念方案的排热能力进行优化，给出了系统几何参数和运行参数的优化方向。结果表明：在所研究参数范围内，适当增加内部和外部换热器传热管径可增加系统排热能力；最佳外/内部换热器传热管数比为1.58。     

Linera analytical one-dimensional model describing the frequency response behavior of shell-and-tube type counterflow heat exchangers with respect to primary and secondary inlet temperature and mass flow perturbations

A linear analytical one-dimensional model is presented. It is used to calculate the frequency response behavior of coolant temperature and/or coolant mass flow on both (primary and secondary) outlet sides of a counterflow shell-and-tube type heat exchanger with respect to perturbations in the corresponding temperature and mass flow parameters at the inlet to the primary and/or secondary side, respectively. To make the heat exchanger model as comprehensive as possible, mass-flow dependent heat transfer coefficients, an exact solution of the heat conduction through the tube walls, and (at least with respect to the coolant mass flow rates) temperature-dependent coolant densities have been taken into account. The resulting digital code TUMHEX has been tested against frequency response measurements on an industrial-size heat exchanger and has shown good results.     

Heat Transfer Characteristic of Airfoil Microchannel Efficient and Compact Heat Exchanger

Supercritical carbon dioxide (S-CO₂) Brayton cycle system is a new type of high-efficiency energy conversion system used in the fourth generation reactor. The microchannel efficient and compact heat exchanger is used in the system as high or low temperature recuperators. Besides, heat transfer performance and flow characteristics of heat exchanger have significant impacts on the overall energy conversion efficiency of the system. In this paper, the heat exchanger model of airfoil structure was established and the CFD method was used to study the influence of different spacing of fins on the overall heat transfer characteristics with S-CO₂ as the working fluid. The results show that the convective heat transfer performance of interlaced fins is better than that of side-by-side arrangement. When the interlaced spacing is half of the parallel spacing, the comprehensive performance of heat exchanger is better with the increase of the parallel spacing. The results of airfoil microchannel heat exchanger were compared with those of the Z-shaped microchannel heat exchanger, which shows that the pressure drop of airfoil microchannel heat exchanger is only 54.174% of the Z-shaped microchannel heat exchanger when the heat transfer capacity increases by 25.67%.     

机翼型微通道高效紧凑换热器流动换热特性

超临界二氧化碳（S-CO₂）布雷顿循环系统是第4代反应堆采用的新型高效热能转化系统，系统采用微通道高效紧凑换热器作为高低温回热器，其流动换热特性对整体系统热能转化效率有着显著影响。本文采用数值模拟方法，以S-CO₂为流动工质，建立机翼型翼片结构的换热器模型，研究翼片的不同间距对流动换热性能的影响。研究结果表明，交错排列翼片的综合流动换热性能优于翼片并排布置，翼片交错间距为左右间距一半时，增加左右间距，换热器流动换热性能更好。将机翼型微通道换热器与折线型微通道换热器模拟结果进行对比分析表明，机翼型微通道换热器在压降仅为折线型微通道换热器54.174%的情况下，换热性能提升了25.67%。     

华龙一号非能动安全壳热量导出系统热工水力特性研究

本文针对华龙一号非能动安全壳热量导出系统（PCS）,基于漂移流模型开发了一套一维自然循环瞬态计算程序。利用该程序对PCS内热工水力特性进行了分析研究,得到PCS自然循环流量、换热系数、换热器进出口温度、上升管路竖直段出口含气率及水箱水位等热工水力参数随PCS换热功率的变化。本文研究结果将为评估华龙一号PCS的换热能力提供可靠工具,对PCS的设计和改进也具有指导意义,并为后续开发能够模拟带有PCS的安全壳内热工水力行为的程序打下基础。     

A thermal hydraulic calculation method of an intermediate heat exchanger of a loop type FBR

This paper describes a thermal-hydraulic calculation of an intermediate heat exchanger (IHX) with the computational fluid dynamics (CFD) code CFX. The motivation of this paper is to clarify a heat transfer degradation phenomenon in the IHX through three-dimensional calculation. The whole IHX of the “Monju” reactor is modeled with three parts, i.e., the primary side, the secondary side and the heat transfer region. Through a partial calculation using these models, the flows on the primary side and the secondary side are shown to be axisymmetric. Therefore, a sector model is adopted for the calculation model in the heat transfer region. The calculated temperatures in the IHX are compared with the measured results using the IHX in the “Monju” reactor. Good agreement is obtained for the predicted outlet temperatures and temperatures on the shell surface. As a result of the CFD calculation, it is evaluated that a heat transfer in the lower plenum on the secondary side is dominant under the low flow rate conditions. This fact contributes to lower the heat transfer coefficient in the IHX when the standard heat exchanger theory is applied to calculate the overall heat transfer coefficient between the primary and the secondary sides.     

Flow and Heat Transfer Characteristics of Swordfish Fin Microchannel

The supercritical carbon dioxide Brayton cycle is a new generation of thermal cycle used in the fourth generation of nuclear energy. As a high or low temperature recuperator of supercritical carbon dioxide Brayton cycle, the thermal hydraulic characteristics of the compact microchannel heat exchanger directly affect the power cycle efficiency. Reducing flow resistance of the temperature recuperator while maintaining high heat transfer efficiency is an important research for microchannel heat exchanger optimization design. The swordfish fin microchannel design considering bionics theory can significantly reduce the flow resistance. In this work, the swordfish fin heat exchanger model was established with supercritical carbon dioxide fluid as the flow medium. The effect of swordfish fin design with different arrangements on heat transfer characteristics was analyzed by three-dimensional numerical simulation. At the same time, the thermal hydraulic characteristics of swordfish fin design were compared with those of traditional commercial Z-shaped microchannel heat exchanger. The results show that under the same Reynolds number, the Nusselt number of the swordfish fin microchannel is twice as much as that of the Z-shaped microchannel, but the pressure drop is only half of that. Therefore, the thermal hydraulic performance of swordfish fin microchannel heat exchanger is obviously better than that of Z-shaped heat exchanger. It is obtained from optimization analysis that the optimal pitches for swordfish fin design is that the L_a＝8 mm along the flow direction, and the L_b＝6 mm perpendicular to the flow direction.